The present invention relates to apparatus for cleavage-cutting brittle material such as ceramics, semiconductor wafers or the like, with the utilization of thermal stress generated by irradiating a laser beam on such brittle material.
As a method of cutting a semiconductor wafer or the like, there is known, for example, a method by which a laser beam focused in a narrow range is irradiated onto a wafer, causing the wafer to be locally dissolved or evaporated, and the laser-beam irradiating position is moved in the cutting direction, thereby cutting the wafer.
In this cutting method using such laser beam, however, the substances dissolved or evaporated by the irradiation of a laser beam stick to the surfaces of devices formed on the wafer such as LSIs, ICs and the like. This results in undesirable effects such as deterioration in the conductivity of the electrodes on the device surfaces.
Even though the laser beam is focused in a narrow range, the diameter of a laser-beam spot can be reduced to only about 10 .mu.m. Accordingly, a cut allowance is inevitable. Further, the material loss due to evaporation or the like cannot be avoided.
To overcome the above-mentioned problems, there has been proposed the following technique. That is, a machining starting point is formed on a wafer by notching, chamfering or the like. A laser beam is irradiated to the wafer in the vicinity of the machining starting point to generate cracks in the wafer extending from the center of the laser-beam irradiation position to the machining starting point. Then, the laser beam is moved along the wafer cutting direction, so that thermal stress due to the laser beam accelerates the cracks, thus cleavage-cutting the wafer.
According to a cleavage-cutting apparatus using the above-mentioned technique, when a laser beam is irradiated to a wafer in the vicinity of the machining starting point, micro-cracks are generated due to compressive stress which acts on the beam center and tensile stress which acts on the periphery around the part on which the compressive stress acts. However, such micro-cracks generate radially. Accordingly, when such micro-cracks generated include micro-cracks along the planned cleavage-cutting line, no trouble is caused. However, if such micro-cracks generated do not include micro-cracks along the planned cleavage-cutting line, the cleavage-cut cannot be accurately determined.
Further, the generated micro-cracks are induced by thermal stress due to the irradiation of a laser beam, so that the thermal stress locally acts on the wafer during such an induction process. Accordingly, there are cases where micro-cracks are newly generated, resulting in the presence of a number of micro-cracks on the wafer cleavage-cut surfaces.
Further, there is required a precision mechanism for precisely relatively moving the wafer and the laser source. In particular, when the cleavage-cutting line is two-dimensional or a curved line, such a mechanism is disadvantageously very complicated.